Eureka!

Lighter than Air

Materials scientist Chi Zhou tames graphene, a supermaterial as fickle as it is promising

By Cory Nealon (BA ’02)

“What’s more exciting, though, is that this process could be an important step toward making graphene commercially viable.”

Chi Zhou, Assistant Professor, School of Engineering and Applied Sciences

Graphene is a wonder material saddled with great
expectations.

Discovered in 2004, it consists of a single layer of carbon
atoms packed together in a honeycomb-like pattern. Among its
unworldly properties, graphene is 1 million times thinner than a
human hair, 300 times stronger than steel, the best-known conductor
of heat and electricity, and, under certain conditions, lighter
than air. These attributes could, among other things, help make
computers faster, batteries more powerful and solar panels more
efficient.

But the material has yet to reach its potential, in part because
it’s hard to manipulate beyond its two-dimensional form. This
conundrum has sent scientists around the world searching for a
reliable way to make 3-D graphene. One approach—pouring
graphene oxide, a gel-like form of graphene, into freezing
molds—has met with partial success. The process works, but
only with simple structures that have limited commercial use.

Some scientists have been working with a 3-D printer. In this
scenario, graphene is mixed with a polymer or other thickening
agent. The combination, when pushed out of the printer’s
inkjets, creates three-dimensional objects. But when the polymer is
removed later by heat, it damages the delicate structure, often
rendering it useless.

Zhou, working with engineers from Kansas State University and
the Harbin Institute of Technology in China, may have finally
solved that problem.

Instead of injecting graphene with thickening agents, the team
uses a modified 3-D printer to combine graphene oxide (graphene
with extra oxygen atoms) and water. The printer deposits layers of
the mixture on a surface cooled to minus 25 C. The graphene freezes
instantly, creating three-dimensional structures, with ice acting
as a support.

After the process is finished, engineers dip the
structures—everything from lattice-shaped cubes to
spiderweb-like orbs—in liquid nitrogen, which strengthens the
bond between the ice and graphene. The structures are then placed
in a freeze dryer, where the ice changes into gas and is removed.
The end result is graphene aerogel, a porous and superlight
material in which the liquid part of the gel is replaced by air,
allowing it to retain its shape at room temperature.

“The structures we built show that it’s possible to
control the shape of graphene in three-dimensional forms,”
says Zhou, a native of China who arrived at UB in 2013.
“What’s more exciting, though, is that this process
could be an important step toward making graphene commercially
viable.”

Chi Zhou with the 3-D printer he uses to make 3-D graphene.

Zhou and his colleagues have made objects with densities as low
as .5 kilograms per cubic meter—or less than half the weight
of air. This near weightlessness could revolutionize the
transportation industry, for one, with the production of cars and
airplanes that are ultralight and thus much more
fuel-efficient.

In addition to advancing electronics, batteries and medical
diagnostic devices, graphene aerogel could have a profound impact
on environmental cleanups. Studies show it can absorb up to 900
times its weight, making the material an incredible tool for
sopping up oil spills.

Possibilities such as these have tantalized scientists since
graphene’s discovery 12 years ago. Now, says Zhou, they may
soon be realized. “We’re getting there,” he says.
“Layer by layer.”